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Adenoviral transduction efficiency of ovarian cancer cells can be limited by loss of integrin beta3 subunit expression and increased by reconstitution of integrin alphavbeta3.

Recombinant adenoviruses expressing a therapeutic gene are currently used in clinical studies for treatment of advanced ovarian cancer. We therefore tested whether the expression level of primary (CAR) and secondary adenovirus receptors (integrins) was predictive of the efficacy of adenoviral gene transfer in ovarian cancer cells. Adenoviral transduction efficiency (ATE) was determined with an E1-deleted adenovirus type 5 expressing beta-galactosidase under a CMV promoter (AdGal). ATE was studied in relationship to the expression level of both CAR (coxsackie and adenovirus receptor) and integrins. A representative sample of 25 permanent human cell lines established from advanced ovarian cancer in our laboratory and the OV-2774 cell line were tested. Overall, ATE increased with increasing titers of AdGal. At a given titer of 50 infectious units per cell, transduction efficiency varied from 6 to 94% among the individual cell lines. All cell lines expressed CAR and integrin alpha(v)beta(5), but no relation between ATE and expression level of CAR or alpha(v)beta(5) integrin was observed. In contrast, cell lines with poor ATE, despite expressing high levels of CAR, lacked expression of integrins alpha(v)beta(3) and alpha(5)beta(1). Reconstitution of alpha(v)beta(3) integrin by reexpressing the beta(3) subunit significantly enhanced ATE of ovarian cancer cells. In ovarian cancer, neither integrins nor CAR alone appear to be potentially useful predictive markers for ATE by serotype 5 adenovirus in clinical gene therapy. A minimum level of CAR necessary for binding of adenoviruses was observed in all tested ovarian cancer cell lines. Loss of alpha(v)beta(3) integrin is frequently associated with advanced stages of ovarian cancer and can significantly reduce ATE.

Adenoviridae↗

The GPIIIa (beta3 integrin) PlA polymorphism in the early development of coronary atherosclerosis.

The GPIIIa (beta3 integrin) is an integral part of two glycoprotein receptors - the GP(IIb/IIIa) fibrinogen receptors in platelets and the GP(V/IIIa) vitronectin receptors in endothelium and vascular smooth muscle cells (vSMC). The PlA polymorphism of the gene for GPIIIa (beta3 integrin) has been suggested to play an important role in the progression of coronary artery disease (CAD) and in coronary thrombosis. Whether the action of the PlA polymorphism is due to differences in platelet aggregability or function of the vSMC and endothelial GPIIIa is not known. The association of the PlA polymorphism with the early, non-complicated atherosclerosis and CAD was studied in the Helsinki Sudden Death Study (HSDS) comprising two independent, autopsy series of altogether 700 middle-aged Caucasian Finnish men (33-70 year) suffering sudden out-of-hospital death. The burden of complicated lesions was greater in men with the A2 allele (heterozygotes or homozygotes for A2) (P=0.01) compared with PlA1/A1 homozygotes in the entire series. To further estimate the role of platelet-independent GPIIIa receptors, we excluded all cases with coronary thrombosis and thrombus-overlaid complicated lesions. In this subset of men, fibrous coronary lesions were more frequent (OR 2.9; P<0.01) in the coronary arteries of PlA1/A1 homozygotes compared with men with the PlA2 allele. Moreover, men with the PlA1/A1 genotype also had more stenotic coronary arteries (P<0.05) compared with men with the A2 allele at this early, non-complicated stage of atherosclerosis. The findings of this study suggest that Pl(A1/A1) homozygotes may be prone to early atherosclerosis and more rapid progression of stable CAD whereas carriers of the PlA2 allele are more prone to thrombotic complications. We hypothesize that the PlA polymorphism may account for the early atherosclerosis by affecting the function of endothelial and vSMC GP(V/IIIa) receptors, whereas the PlA polymorphism on platelet GP(IIb/IIIa) receptors may play a major role in coronary thrombosis.

Adult↗

Cytotoxic T lymphocytes express a beta3 integrin which can induce the phosphorylation of focal adhesion kinase and the related PYK-2.

Fibronectin has been shown to stimulate tyrosine phosphorylation of a number of proteins in the 115-125 kDa range and facilitate degranulation by alloantigen-specific cytotoxic T lymphocyte (CTL) clones in response to substimulatory amounts of anti-CD3 or anti-T cell receptor (TCR). The current study was initiated to further characterize integrin expression and usage by these CTL clones. We demonstrate that vitronectin and fibrinogen, but not laminin or collagen, are also able to both facilitate degranulation in the presence of substimulatory anti-CD3 and stimulate tyrosine phosphorylation of these 115-125-kDa proteins, with a 115-kDa protein being the most prominently phosphorylated. These results implicate the expression and usage of the vitronectin receptor, alpha beta3 integrin, by these CTL clones. We demonstrate by both flow cytometry and immunoprecipitation that CTL clones do in fact express beta3 integrin. Immobilized antibody to beta3 stimulates the phosphorylation of the 115-125-kDa proteins, suggesting that engagement of beta3 transmits the same signal into these cells as fibronectin or vitronectin. The fibronectin and vitronectin-induced phosphorylation as well as adhesion to either fibronectin or vitronectin can be significantly inhibited with antibodies to beta3 integrins. Finally, we are able to immunoprecipitate 115-kDa proteins with antiserum to focal adhesion kinase and a related kinase, called PYK-2, that becomes phosphorylated in response to vitronectin or immobilized anti-beta3. Taken together, these results demonstrate that CTL express and use beta3-integrins as signaling molecules which can augment TCR-mediated stimulation.

Animals↗

Differential regulation of Rho GTPases by beta1 and beta3 integrins: the role of an extracellular domain of integrin in intracellular signaling.

Integrins mediate cell adhesion and signal transduction at focal adhesions. Here we investigate the roles of integrin beta subunits in the regulation of actin cytoskeletal structure and the activities of Rho and Rac. The overexpression of beta3 integrin in Chinese hamster ovary cells enhances Rho activity and stress fiber formation, whereas the overexpression of beta1 integrin increases Rac activity and lamellipodia formation. The overexpression of a mutant beta1-3-1 integrin, in which the extracellular I-domain-like sequence of beta1 integrin has been replaced with the corresponding sequence of beta3 integrin, also enhances Rho activity and the formation of stress fibers. Our results demonstrate that beta1 and beta3 integrins differentially regulate the activities of Rho family GTPases and that the extracellular domains of integrin beta subunits play a critical role in transducing the extracellular ligand-binding information into specific intracellular signaling events.

Actins↗

Human carotid artery smooth muscle cells rarely express alpha(v)beta3 integrin at sites of recent plaque rupture.

Fibrin(ogen) is the major matrix ligand for beta3 integrins. If alpha(v)beta3 is the major receptor for fibrin(ogen) on intimal smooth muscle cells, we might expect to see this integrin associated with fibrin(ogen). Eighty-four specimens obtained from endarterectomies of 14 patients were studied. Fibrin was frequently observed in carotid intima even at the non-atherosclerotic areas. As for beta1 and beta3 integrins, beta1 was predominant in intima. The alpha(v)beta3 integrin expression was less frequent than alpha5beta1, another receptor for fibrin(ogen), in diffuse intimal thickening, fibrous cap and advanced plaques. Furthermore, alpha(v)beta3 was generally negative on smooth muscle cells in recent plaque ruptures. In conclusion, we suggest more attention should be paid on abundant fibrin matrix in intima. Histologically, the alpha5beta1 integrin rather than the alpha(v)beta3 is the major receptor for fibrin in intimal smooth muscle cells.

Adolescent↗

Beta3 integrin activation improves alphavbeta3-mediated retraction of fibrin matrices.

BACKGROUND: Integrins are heterodimeric transmembrane glycoproteins that mediate cell interactions with the extracellular matrix. In vivo, integrin affinity can be modulated by intracellular signaling events. This can be simulated by a point mutation (D723R) in the cytoplasmic tail of the beta3 integrin subunit which results in constitutive activation. The effects of beta3 integrin activation on the function of alphavbeta3, an integrin which is important to the adhesive events of multiple cell types, were addressed using Chinese hamster ovary cells expressing either the wild-type alphavbeta3 integrin or the mutant alphavbeta3(D723R). The interactions of these cell lines with fibrin matrices were compared. METHODS: Receptor expression levels were confirmed by FACS analyses using a monoclonal anti-alphavbeta3 antibody. Cell attachment to fibrin-coated dishes was determined after 1 h by fixation and crystal violet staining followed by elution of the dye and OD measurement. Fibrin clot retraction was measured by culturing cells in fibrin clots for 24 h. The clots were detached from the dish and the surface area was calculated at individual time points. RESULTS: CHO alphavbeta3(D723R) cells displayed a greater than twofold increase in attachment to fibrinogen or to fibrin matrices when compared to wild-type transfectants. Further, CHO alphavbeta3(D723R) cell retraction of fibrin matrices was significantly greater at nearly all time points. CONCLUSION: Activation of the beta3 integrin subunit significantly improves the interaction of alphavbeta3 with fibrin and may play a role in the integrin-mediated signaling events which occur following vascular injury.

Animals↗

A naturally occurring point mutation in the beta3 integrin MIDAS-like domain affects differently alphavbeta3 and alphaIIIbbeta3 receptor function.

We have investigated the effect of a new Leu196Pro mutation, identified in the MIDAS-like domain of the beta3 integrin subunit in a patient with type II Glanzmann thrombasthenia, on beta3 integrin receptor function. Expression of the mutant beta3Pro196 subunit in CHO cells, either associated with recombinant human alphaIIb or alphav, resulted in normal biosynthesis of beta3 and heterodimerization with alphav or alphaIIb, but selectively interfered with alphaIIbbeta3 maturation and transport to the cell surface. Functional analysis of the beta3 mutant receptors revealed strong inhibition of alphavbeta3-mediated cell spreading on immobilized fibrinogen, focal contact formation, p125FAK phosphorylation and fibrin clot retraction, as opposed to normal alphaIIbbeta3-mediated cell interaction with immobilized fibrinogen, focal contact translocation and signaling. In contrast, antibody- or DTT-activated mutant aIIbbeta3 was unable to bind soluble fibrinogen or the ligand mimetic PAC-1 monoclonal antibody, but underwent a conformational change following RGD peptide binding as demonstrated by AP5-LIBS epitope expression. These results suggest that (1) the highly conserved TL196T motif in the beta3 integrin subunit is located in a domain structurally important for the exposure of a functional binding site for soluble fibrinogen; and (2) that the MIDAS-like contact site in beta3 is not involved in alphaIIbbeta3-mediated cell adhesion to immobilized fibrinogen, while it is essential for alphavbeta3-mediated interaction with this ligand.

Amino Acid Sequence↗

Ets-1 and integrin beta3 for lung metastasis from colorectal cancer.

Ets-1 functions as tissue-specific transcription factor and plays an important role in cell proliferation, differentiation, angiogenesis, and apoptosis. To elucidate the involvement of Ets-1 in lung metastasis from colorectal cancer, immunohistochemical analysis was performed on 51 colorectal cancer patients (22 with lung metastasis and 29 with advanced colorectal cancer showing no recurrence for at least 5 years after surgery). Tumorous and stromal Ets-1 immunoreactivity was evaluated. Ets-1 protein was demonstrated within stromal fibroblasts, myofibroblasts and capillaries, and also within carcinoma cells. Stromal Ets-1 immunoreactivity in primary colorectal cancer was statistically correlated with lung metastasis (p<0.05). In primary colorectal cancer, a significant association was observed between stromal Ets-1 immunoreactivity and vascular integrin beta3 expression (p<0.01). In the cases with lung metastasis, vascular integrin beta3 index in lung metastases was significantly diminished compared with primary tumors or liver metastases (p<0.01). In contrast, stromal or tumorous Ets-1 expression did not change. In a multivariate model using logistic stepwise regression analysis, vascular integrin beta3 and stromal Ets-1 overexpression were significantly and independently related to lung metastasis. Stromal Ets-1 and/or vascular integrin beta3 may be useful markers for risk of lung metastasis from colorectal cancer.

Adult↗

An allosteric Ca2+ binding site on the beta3-integrins that regulates the dissociation rate for RGD ligands.

Here we use a model RGD-containing ligand to study how Ca2+ and Mg2+ regulate ligand binding to beta3-integrins. Fab-9, an antibody that contains an optimized RGD loop in its antigen binding site (Barbas, C. F., Languino, L., and Smith, J. W. (1993) Proc. Natl. Acad. Sci. U. S. A. 90, 10003-10007), was used as the model ligand. Across a physiologic range of Mg2+, Fab-9 bound to both alphavbeta3 and alphaIIbbeta3 with a monophasic binding isotherm. Across the same range of Ca2+, the binding of Fab-9 to the beta3-integrins was biphasic. Low concentrations of Ca2+ (microM) promoted the binding of Fab-9. Higher concentrations of Ca2+ (m) blocked Fab-9 binding. These data suggest that Ca2+ binds to two distinct classes of sites on the beta3-integrins, with the low affinity Ca2+ binding site(s) being an inhibitory site. We designate this inhibitory site(s) as the I site. Further biochemical characterization showed that the I site has the following characteristics: 1) it is specific for Ca2+; 2) it is allosteric to the ligand binding site; 3) its occupation increases the dissociation rate between integrin and RGD ligand; and 4) occupation of the I site can induce cellular deadhesion.

Allosteric Site↗

Activation of alphav beta3 integrin on human osteoclast-like cells stimulates adhesion and migration in response to osteopontin.

Integrins mediate cell adhesion and can induce different cellular responses, including changes in intracellular pH, changes and oscillation in intracellular free calcium, and protein phosphorylation on tyrosine. During bone resorption, the integrin alphav beta3 regulates adhesion of osteoclasts to bone extracellular matrix proteins, such us osteopontin (Opn). Adhesion via alphav beta3 is followed by osteoclast polarization onto the bone surface and by the onset of bone resorption. To characterize these events at the molecular level, we investigated the state of activation of alphav beta3 on the human osteoclast-like cell line GCT23 using the monoclonal antibody AP5 which binds to and can induce, under low calcium conditions, activated alphav beta3. By flow cytometry, approximately 50% of alphav beta3 on the surface of the osteoclast-like cell line GCT23 was reactive with AP5 and was therefore in the activated state. Incubation with AP5 in the presence of low calcium concentrations increased activated alphav beta3 to 90-100%. Activation of alphav beta3 increased the efficiency of GCT23 adhesion to Opn by 2-fold. Furthermore, haptotactic migration on Opn was also enhanced about 40% compared to control. We propose that changes in the activation state of alphav beta3 may be a regulation point for osteoclasts during bone resorption.

Antibodies, Monoclonal↗

Phosphorylation of beta3 integrin controls ligand binding strength.

The cytoplasmic domain of beta(3) integrin contains tyrosines at positions 747 and 759 in domains that have been implicated in regulation of alpha(v)beta(3) function and that serve as potential substrates for Src family kinases. The phosphorylation level of beta(3) integrin was modulated using a temperature-sensitive v-Src kinase. Increased beta(3) phosphorylation abolished alpha(v)beta(3)- but not alpha(5)beta(1)-mediated adhesion to fibronectin. alpha(v)beta(3)-Mediated cell adhesion was restored by the expression of beta(3) containing Y747F or Y759F mutations but not by wild type beta(3) integrin. Thus, phosphorylation of the cytoplasmic domain of beta(3) is a negative regulator of alpha(v)beta(3)-fibronectin binding strength.

Antigens, CD↗

Protein structure prediction and biomolecular recognition: from protein sequence to peptidomimetic design with the human beta3 integrin.

Computational tools can bridge the gap between sequence and protein 3D structure based on the notion that information is to be retrieved from the databases and that knowledge-based methods can help in approaching a solution of the protein-folding problem. To this aim our group has implemented neural network-based predictors capable of performing with some success in different tasks, including predictions of the secondary structure of globular and membrane proteins, the topology of membrane proteins and porins and stable alpha-helical segments suited for protein design. Moreover we have developed methods for predicting contact maps in proteins and the probability of finding a cysteine in a disulfide bridge, tools which can contribute to the goal of predicting the 3D structure starting from the sequence (the so called ab initio prediction). All our predictors take advantage of evolution information derived from the structural alignments of homologous (evolutionary related) proteins and taken from the sequence and structure databases. When it is necessary to build models for proteins of unknown spatial structure, which have very little homology with other proteins of known structure, non-standard techniques need to be developed and the tools for protein structure predictions may help in protein modeling. The results of a recent simulation performed in our lab highlights the role of high performing computing technology and of tools of computational biology in protein modeling and peptidomimetic design.

Databases, Factual↗

Role of beta1 and beta3 integrins in human smooth muscle cell adhesion to and contraction of fibrin clots in vitro.

The degree of lumen narrowing in advanced lesions correlates poorly with the amount of intimal mass accumulated in the atherosclerotic plaque. As an alternate mechanism of stenosis, we propose that human smooth muscle cells bind to fibrin deposited in the matrix and exert contractile forces to cause a narrowing of the lumen. In the present study we demonstrated in vitro that human newborn aortic smooth muscle cell lines can contract and adhere to fibrin clots composed of either fibronectin-depleted plasma ("plasma") or recombinant fibrin. By using neutralizing antibodies and RGD peptides, we showed that members of the integrin family mediated the interaction between human newborn smooth muscle cells and fibrin. Neutralizing antibodies against the integrin alphavbeta3 (c7E3 Fab and LM609) did not inhibit either plasma clot contraction or recombinant fibrin clot contraction by human newborn smooth muscle cells. In contrast, antibodies against alpha5, beta1, and alpha5/beta1 inhibited contraction of clots composed of either plasma or recombinant fibrin. Anti-alphavbeta3, anti-alphav, anti-alpha5, anti-beta1, and anti-alpha5beta1 antibodies inhibited human newborn smooth muscle cell adhesion to plasma clots; however, only anti-alpha5, anti-beta1, and anti-alpha5beta1 antibodies significantly inhibited adhesion to recombinant fibrin. While the linear RGD peptides had no effect, the cyclic peptide penRGD inhibited adhesion to plasma clots and recombinant fibrin. However, it did not block contraction of recombinant fibrin clots. These results suggest that during the interaction of human newborn smooth muscle cell lines with fibrin, alpha5beta1 plays a significant role. This interaction is of potential interest as a target for efforts to block vascular contraction.

Antibodies↗

Identification of critical residues for ligand binding in the integrin beta3 I-domain by site-directed mutagenesis.

To define the structural basis of ligand recognition by alphaIIb beta3, we conducted site-directed mutagenesis of residues located on the top surface of the beta3 I-domain that is homologous to the I-domain of several alpha subunits and contains a putative ligand binding site. Here we identify D158 and N215 in beta3 as novel residues critical for ligand binding. Alanine substitution of D158 or N215 abolished binding of a ligand-mimetic antibody and fibrinogen to alphaIIb beta3 induced by different types of integrin activation. CHO cells expressing recombinant alphaIIb beta3 bearing D158A or N215A mutation did not adhere to fibrinogen. These mutations had the same effect on ligand binding to another beta3 integrin, alphaVbeta3. Compared to the alphaI-domain structure, the betaB-betaC loop containing D158 in the beta3 I-domain is quite different in length and sequence. These results suggest that the structure for ligand recognition is different in the betaI- and alphaI-domains.

Animals↗

Suppression of the antibody response to a polymorphic peptide from the platelet alloantigen integrin beta3 with low molecular weight antigen arrays.

The allelic human platelet alloantigens PIA1/PIA2 are determined by a 33 Leu-Pro substitution in the second disulfide loop of the integrin beta3 subunit of the fibrinogen receptor, alphaIIb beta3 (GPIIb-IIIa). Alloantibodies to PIA1 cause neonatal alloimmune thrombocytopenia. We studied the suppression of specific Ab production to a disulfide-looped peptide spanning the polymorphic region of integrin beta3, 24AWCSDEALPLGSPRCD39 (LPL). Mice immunized with LPL coupled to OVA (LPL-OVA) produced Abs specific for LPL. When immunized animals were injected with low m.w. dextran heavily derivitized with LPL (Dex(low)LPL(high)), levels of Ab to LPL fell immediately and remained low 1 mo later. Both high affinity and total Abs were affected. Arrays with lower peptide density or a high m.w. backbone did not induce well sustained suppression. Abs to OVA were unaffected by the arrays. Naive mice given Dex(low)LPL(high) were tolerant to subsequent immunization with LPL-OVA. In transfer experiments, irradiated recipients of spleen cells or purified 8 cells from animals suppressed with Dex(low)LPL(high) did not respond to LPL-OVA. Spleen cells from suppressed animals did not suppress the response to LPL-OVA in recipients of immune B cells. These results demonstrate that peptide arrays, by a mechanism sensitive to molecular configuration, induce tolerance to peptide immunization and suppress an ongoing, high affinity Ab response. Peptide arrays induce the elimination or irreversible anergy of specific memory B cells and do not require a non-B spleen cell population to maintain suppression.

Amino Acid Sequence↗

Spironolactone increases integrin beta3 gene expression in kidney and heart muscle cells.

In clinical trials of heart failure, spironolactone, an antagonist of the mineralocorticoid receptor (MR), reduced mortality rates by unknown mechanisms. We hypothesized that spironolactone functions by upregulating expression of certain cardiovascular genes. An RNA differential display technique was used to identify genes whose expression was increased by spironolactone in an Xenopus kidney epithelial cell line (A6), a known target of aldosterone. We found that integrin beta3 gene expression was increased by spironolactone, and reversed by aldosterone or dexamethasone in a dose dependent manner. Competition binding studies and RT-PCR indicate the presence of MR in A6 cells, suggesting that regulation of expression occurred primarily through MR. Spironolactone also increased integrin beta3 expression in rat neonatal cardiomyocytes. In summary, spironolactone increases integrin beta3 gene expression in kidney epithelial cells and cardiomyocytes. The findings suggest new mechanisms for spironolactone actions with possible relevance to treatment of heart disease.

Aldosterone↗

Potential role of a new anti-beta3 integrin antibody in the development of intimal hyperplasia after vascular surgery: an in vitro smooth muscle cell model.

The occurrence of intimal hyperplasia after vascular surgery is an ongoing concern in current clinical practice. Among the many factors involved in the development of this pathology, platelet adhesion and myointimal proliferation play a major role. Both these processes are mediated by integrins (mainly alphavbeta3 integrins). Over the past years, several substances have been designed to delay or inhibit the cell proliferation that leads to hyperplasia and mainly include monoclonal antibodies directed against integrins. The aim of the present study was to evaluate the effects of an antibody denoted P37 (anti beta3 integrin) on human smooth muscle cells (SMC) and its role in blocking the B3 subunit. To this end, SMC from human umbilical artery were cultured in the presence or absence of the cell substrate vitronectin (VN) and incubated with P37. After 4 days of treatment, determination was made of cell proliferation and migration. Smooth muscle cells grown on VN showed increased proliferation and migration compared to control VN-free cultures. However, the presence of P37 in the culture medium inhibited proliferation and reduced migration. Combined treatment with VN and P37 led to improved proliferation but VN was unable to reverse the effects on migration observed in the former cultures. Results suggest that in vitro, P37 is capable of blocking human SMC beta3 integrins and thus impedes cell proliferation and migration These findings may have clinical implications related to modulation of the development of hyperplasia.

Antibodies↗

In vitro and in vivo effects of a cyclic peptide with affinity for the alpha(nu)beta3 integrin in human melanoma cells.

Expression of the integrin alpha(nu)beta3 has been shown to be associated with increasing metastatic potential in malignant melanoma. It also has a functional role on vascular endothelial cells during angiogenesis. The cyclic oligopeptide cRGDfV is known to bind with high affinity to alpha(nu)beta3. We have investigated the cellular effects of cRGDfV on a panel of human melanoma cell lines in vitro and also on the A375 melanoma cell line growing as xenografts in nude mice. cRGDfV is a potent inhibitor of alpha(nu)beta3-mediated cell adhesion, however, we have found no convincing evidence that integrin ligation by cRGDfV induces apoptosis in melanoma cell lines. However, cRGDfV when administered subcutaneously into nude mice did inhibit the growth of A375 melanoma xenografts. Histological examination of the tumours indicated that this effect was primarily one of angiogenesis inhibition. The results suggest that agents which target the alpha(nu)beta3 integrin may have a useful role as anti-angiogenesis agents in clinical oncology, but that they may not exert a direct effect on alphavbeta3-expressing tumour cells.

Animals↗